Electrical-distribution system



July 8, 1930.

ELECTRICAL DISTRIBUTION SYSTEM Filed Dec. 1925 A A A;

' WITN s E v INVENTOR Patented July 8, 1930 UNITED STATES PATENT OFFICEI EARL R. EVANS, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TOGENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORKELECTRICAL-DISTRIBUTION SYSTEM Application flledDecember 2, 1925. SerialNo. 72,718.

My invention relates to electrical distribution systems and apparatusand particularly to systems embodying means for controlling or modifyingthe transmission characteristics thereof under predetermined conditions.

In general terms, it is one object of my invention to provide anelectrical power distri- A still further object of my invention is toimprove, the detailed construction of protective apparatus forelectrical systems.

In accordance with my invention, as aplied to a power distributioncircuit a reactor liaving a winding connected in series relation withthe distribution circuit and a short-circuited secondary winding isemployed. The secondary winding is short-circuited through acurrent-limiting device, such as a highlyevacuated thermionic tube or agas or Vaporfilled tube. The tube is so constructed that its resistanceis a minimum at normal fullload current or other desired condition. Un

der abnormal conditions, the resistance of the tube is greatl increasedso that the secondary winding no longer functions as a short-circuitedwinding.

Under normal conditions, the effective impedance of the reactor is lowbecause of the short-circuited secondary winding. When the resistance.of the secondary winding increases, however, the effective impedance ofthe reactor is increased, thereby modifying the transmissioncharacteristics of the systems but may also be applied to other systems,in its application to power-transmission systems but may also be appliedto other system, such as signalling or communication systems.

For ordinary applications, any electrical discharge, device having acurrent-limiting characteristic may be used in combination with thereactor. Thermionic tubes either of the highly evacuated type operatingwith a pure electron discharge or of the gas-tilled arc type utilizingionization principles are examples of suitable current-limiting devices.For certain applications, either of these types of thermionic tubes maybe used, but for the protection of long, high-voltage circuits, I preferto use the gas-filled tube because this tube has a smaller resistancefor normal currents than the highly evacuated tube and a higherresistance than normal for either small a plied voltages or over-voltagesurges.

nder light-load conditions, such high-voltage circuits have a largerratio of capacity voltage-drop to inductive voltage-drop than under fullload conditions which tends to make the voltage regulation of the linepoor. The use of an arc device in connection with such a line not onlylimits the excessive current flow resulting from a fault on the system,but also increase the effective induc tance of the circuit duringlight-load periods, thereby improving the inherent voltage regulation-ofthe circuit.

For a clearer understanding of my invention, reference should be had tothe accompanying drawings, of which Figure 1 is a view of a portion ofan elec trical distribution system embodying the same;

Fig. 2 is a detailed view of an improved current-limiting deviceapplicable to the system shown in Fig. 1;

Fig. 3 is a similar view of another modification;

Fig. 4 is a schematic diagram of a highvoltage transmission line havingreactors disposed therein at a plurality of points; and

Fig. 5 is a detailed view showing an arrangement of the reactor upon atower or supporting structure of a high-voltage trans mission line.

Refzrring to Fig. 1, an electrical distribution system comprises analternator l or other source of alternating current and a transmissioncircuit 2 having a reactor 3 in series therewith for controlling ormodifying the load current under predetermined conditions. In accordancewith my invention, the reactor 3 is so designed as to offer a minimumimpedance to the load current at a predetermined value of current-forinstance, that corresponding to full-load output of the generator 1, anda greater impedance to smaller or larger currents, or both.

The reactor 3 comprises a main winding or section 4; in series with thetransmission circuit 2 and an auxiliary or secondary winding 5inductively related to the winding 4. As the main winding 4 may besubjected, in the case of a short-circuit or overload on thetransmission circuit, to a current many times larger than the normalfull-load current, it comprises substantial conductors embedded in orsupported by refractory insulating members 6 of porcelain or othersuitable material. In this manner, the winding is braced against themagnetic forces produced by the excessive currents. Suitable spaces oropenings 7 may be provided for ventilation purposes, if appreciable heatis developed in the winding in operation.

Since one object of my invention is to limit, to a greater extent thanhas heretofore been possible, the current traversing the reactor underabnormal conditions, the winding 4 and insulating members 6 may besmaller and less substantial and expensive than those commonly used. Theauxiliary winding 5 carries only a limited current under all conditions.It does not require such careful insulation and bracing as the mainwinding, therefore, and it has been deemed unnecessary to illustrate thesupporting elements thereof.

A plurality of current-limiting devices 8 are connected across theterminals of the secondary winding 5. As shown, these devices comprise acathode 9 and an anode 1O enclosed in a sealed envelope 11. The cathode9 may be of the filamentary type, as shown, and heated by any suitablesource of current, such as the circuit 2. The envelope 11 may be highlyevacuated or may contain a gas or vapor at such pressure as to producean arc discharge between the electrodes of the desired characteristicsdepending upon the applied voltage. In the case of a highly evacuatedtube, the current traversing the device is limited by the number ofelectrons emitted by the cathode and will not exceed a predeterminedvalue irrespective of the applied voltage. In the case of thearc-discharge device, the cathode or other source of electrons serve asan ionizing means and the envelope may contain mercury vapor or argon orother inert gas at such pressure as to produce an arc of the desiredcharacteristics, such as a low voltage drop.

Either of these devices will, therefore, serve as a current-limitingmeans if an excessive current traverses the main winding of the reactor3. Furthermore, the gas-filled tube will present a high resistance tothe passage of current when the applied voltage is less than theionization potential of the gas or insuflicient. to strike the arc, andthe reactor 3 will therefore possess a greater impedance for smallvalues of current than for full-load current, when embodying anarc-discharge tube.

In the arc-discharge device, the current is only momentarily limited invalue, as the current will build up in time until the voltage dro acrossthe tube is of the same order as the initial drop. Accordingly, withthis type of tube, a fuse 12 in series with the tube or a. quick-actingoverload circuit-interrupter 13 in the main circuit is used, and thetube is only utilized to limit the current momentarily, or during thetime required for the fuse or circuit-interrupter to become operative.\Vhile this time may be very short, it is often a critical period in thecase of sudden large surges of current. It will be apparent therefore,that apparatus embodying the invention provides protection againstsurges not afforded by circuit-interrupters and the like.

A plurality of tubes may be connected in parallel, as indicated in Fig.1, when the normal current in the secondary winding 5 is large. versedin order to equalize the resistance to the flow of current in eitherdirection through the winding 5.

The use of oppositely connected tubes may be avoided by providing thetube with two cathodes, as shown in Fig. 2. The tube shown in Fig. 2 issimilar to those shown in Fig. 1, except that two filamentary cathodes15 and 16 are supported from opposite ends of the tube by the supportingleads 17, on which are disposed metal discs or plates 18. As shown, theleads 17 are connected to conductors 19 adapted to be connected to anauxiliary source of current for heating the oathode to incandescence.The disc members 18 serve to cool the cathodes by conduction andradiation, particularly when a gas filling is used andthe current in thearc is abnormally high. Certain of the disc members 18 may be disposedin such close proximity to the cathodes 15, 16 as to serve as anodes orterminals for the arc discharge or the electrons emitted by the oppositecathodes.

Another form of current-limiting device is illustrated in Fig. 3. Thedevice comprises a filamentary cathode 25 centrally disposed in acylindrical anode 26, both anode and cathode being contained in thesealed envelope 27. The electrodes 25 and 26 are connected to theterminals of the secondary winding 5 of the reactor 3. Preferably one ormore opp0sitely-connected pairs of thermionic tubes are provided, as inFig. 1, although only one is shown. A magnetic field transverse to thecurrent flow between the electrodes is provided by a field winding 28connected to a As shown, half of the tubes are recurrent transformer 29in the line circuit. lVhen the current exceeds a predetermined value,the strengthened magnetic field increases the impedance of thecurrent-limiting device, thereby increasing the impedance of the reactor3. An auxiliary field winding 30' controlled by an under-current relay31 in the circuit of the current transformer 29 may also be provided, ifdesired, to increase the impedance of the device when the -load currentis less than a predetermined value. The devices shown in Figs. 1 and 2may be similarly provided with a field winding or so disposed withrespect to the reactor winding 4 as to control or extinguish the areunder excessive current conditions.

My invention is especially adapted for the protection of long,high-potential transmission circuits against abnormal surges of currentor short-circuits. Such a circuit is represented diagrammatically inFig. 4, in which a generator 35 is connected, through a stepuptransformer 36, to the circuit 37. At some distant point, a load 38 isconnected to the transmission circuit through a step-down transformer39. A plurality of reactors 3, similar to those shown in the precedingfigures, are connected in the transmission circuit at suitableintervals. In some cases, a single reactor may be found sufficient, butit is believed that the use of distributed reactors will serve toconfine surges of current to short portions of the circuit and therebyprovide the maximum protection.

- The impedance devices 3 have a minimum impedance at a predeterminedvalue,of current, for instance, that corresponding to the maximum loadcarried by the system under normal conditions, and a relativelylarge-impedance for currents in excess of said predetermined current.Excessive currents are therefore limited by the increased impedance ofthe circuit. The conductors and switching apparatus may be less rug" edand designed with a smaller factor of saf aty, while the occurrence offaults on one portion of a complicated network will not disturb the-restof the system to the same extent as heretofore.

The increased im edance is available instantaneously and t 'ereforeprovides more complete protection than is rovided by thecircuit-interrupters common y employed to isolate faulty circuits, asthe latter require an appreciable period of time for their operation. Insome cases, it is even possible to omit the circuit-interruptersentirely where the impedance of the system is of sufficient magnitude tolimit the current under all conditions to a safe value. Furthermore,when arc-discharge devices re uiring a definite initial potential areutilized, the system possesses a relatively large inductive impedance atlight loads. A long transmission circuit which has a high capacitivereactance ordinarily has a poor voltage regulation at light loads. Theuse of impedance of such character as to increase the inductivereactance or resistance of the circuit in connection with such a systemimproves the inherent voltage regulation of the system.

As shown in Fig. 5, the impedance may be combined with the supportingstructure of a transmission line. As an example of this construction, atower 40, of which only the upper portion is shown, for supporting aline conductor 41 upon the insulators 42 and 43 is adapted to carry thesecondary winding 5 upon the cross-bar 44 thereof. The main winding 4 inseries relation with the line conductor is carried in the axis of thewinding 5 by a strain insulator 45 of wood, for example, supported byand between the insulators 42 and 43. The winding 5, if supported insuch manner that there is no possiility of accidental contact with thewinding 4, need not be insulated for the line of the system.

Various modifications and other uses of apparatus embodying the generalprinciples disclosed above will occur to those skilled in the art and,if within the scope of the appended claims, shall be considered withinthe scope of the present invention.

I claim as my invention:

1. An electrical distribution system comprising a circuit and a reactiveimpedance device in said circuit having a smaller impedance at apredetermined load current than for either smaller or larger currents.

2. An electrical distribution system comprising a transmission circuitof high capacity reactance and means for im roving the light-loadregulation of the circuit, said means including an electrical dischargedevice coupled to the circuit.

3.-An electrical distribution system comprising a high-voltage circuitof such length that-its capacity reactance is relatively high and aplurality of spaced impedance devices therein, each of which has avariable impedance which is less at full-load current than when arelatively small current traverses the circuit, said impedance devicesbeing so distributed along the circuit as to improve the li ht-loadregulation of the system.

4. he combination of a two-electrode therpotential mionic device havinga constantly energized cathode and connected to said secondary winding.I

6. A reactor-comprising a primary winding and a secondary winding sorelated thereto as to have a voltage induced therein in accordance withthe current traversing said primary winding, and a continuously excitedarc-discharge device connected to said secondary winding.

7. A reactor comprising a winding and a thermionic device in circuittherewith, means for altering the im edance of said reactor comprisingmeans Ior establishing a magnetic field through said thermionic device.

8. Electrical controlling apparatus of the character describedcomprising a winding and a magnetically controlled thermionic device sorelated to said winding as to alter the impedance thereof depending uponthe current traversing the said winding.

9. A reactor having an arc-discharge device operatively associatedtherewith and disposed in such relation thereto that the magnetic fieldof the reactor influences the impedance of said device.

10. In an alternatin -current circuit, a device including twoindirctively related windings, one connected to said circuit, and acontinuously excited electrical discharge device of the ionization typewhich breaks down and commences to discharge at a certain criticalpotential connected in series relation with the other winding.

11. In combination with a power line conductor, current-controllingapparatus embodying an electric discharge device spaced from but sodisposed in relation to the line conductor that the impedance of thedevice is influenced by the magnetic field surrounding said conductor.

12. A variable-impedance device comprising two inductively relatedwindings and an arc-discharge device embodying a heated cathode element,said arc-discharge device being connected to one of said windings.

13. A variable-impedance device comprising two inductively relatedwindings, an arcdischarge device associated therewith and means forlimiting the current traversing said arc-discharge device.

14. In an alternating-current circuit, a device including twoinductively related windings, one connected to said circuit, and anelectrical discharge device of the ionization type in which thedischarge takes the form of an arc and which breaks down and commencesto discharge at a certain critical potential connected in shunt relationwith the other winding, said discharge device embody ing a heatedcathode.

15. In combination with a power line conductor, current-controllingapparatus em-.

bodying an electric discharge device spaced from but so disposed inrelation to the line conductor that the impedance of the device isinfluenced by the magnetic field surrounding said conductor, said deviceembodying a heated cathode.

16. Electrical controlling apparatus of the character describedcomprising a main winding, a secondary winding inductively relatedthereto and an arc-discharge device connected to said secondary winding,said device embodying a discharge ath and a heated cathodehfor ionizingat east a portion of said pat 17. Electrical controlling apparatus ofthe character described, comprising two inductively related windings andan arc-discharge device embodying a. solid ionizing cathode maintainedat an elevated temperature, said device being connected in shunt to oneof said windings.

18. In an electrical circuit, controlling means embodying a.space-discharge device comprising a heated cathode and arranged tointeract on the circuit to affect the current flowing therein, saiddischarge device being of the type which has substantially infiniteimpedance for applied voltages below av predetermined value and a lowimpedance for a greater applied voltage.

19. In combination, an electric circuit, a reactor connected in saidcircuit, an electric discharge device connected in circuit with saidreactor, means energized in accordance with the current in said circuitfor establishing a magnetic field through said electric dischargedevice, additional means for establishing a magnetic field through saidelectric discharge device, and means for establishing an energizingcircuit for said additional means when the current in said circuit isbelow a predetermined value.

20. In combination, an electric circuit, a reactor connected in saidcircuit, an electric discharge device connected in circuit with saidreactor, means energized in accordance with the current in said circuitfor establishing a magnetic field through said electric dischargedevice, additional means for establishing a magnetic field throu h saidelectric discharge device, a source of current independent of saidelectric circuit for energizing said additional means, and currentresponsive means in said circuit for connecting said additional means tosaid source of current when the current in said circuit is below apredetermined value.

In testimony whereof, I have hereunto subscribed my name this 25th dayof November,

EARL R. EVANS.

CERTIFICATE OF CORRECTION.

Patent No. 1,770,334. I Granted July 3, 1930', m

' EARL R. EVANS.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,line 46, beginning with the word "systems" strike out all to .andincluding the word "system" end of line 49, and insert instead system.Obviously the invention is not limited in its application topower-transmission systems but may also be applied to other systems;same page, line 75, for the word "increase" read increases; page 2, line58, for the word "serve" read serves, and line 117, for "cathodes" readcathode; and that the I'said Letters Patent should be read with thesecorrections therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 23rd day of September, A. D. 1930.

' M. J. Moore, (Seal) 1 Acting Commissioner of Patents.

